I completely agree, and I think this is a necessary improvement over having to use low-level file permissions to mark the .appimage as executable. This is the closest thing currently possible to zipped app bundles on the mac, which I’m amazed that none of the linux environments have copied yet.
The executable bit is a low-level function, meant to separate executables from data files in shell scripts and terminal prompts. It’s not user-friendly enough to pass through to users in a GUI environment.
If the user downloads something with an executable file extension and makes a specific intention to run it by double-clicking, then they are expressing their intent. Ideally the GUI would present a warning and/or authentication prompt the first time an executable is double-clicked before running it. Forcing them to chmod or get deep into a unix-level permissions dialog is a bit cruel.
As it stands, it sounds like a tar.gz file with a shell script launcher is more user friendly than an AppImage, because all the user needs to do is extract the file, then double-click to launch. I think the extraction could even be a bonus, because it gives the user a chance to unpack the app in a location of their choice. The only thing to worry about is the user’s unarchiver stripping the executable bits, but presumably that can be covered by a README file which is referenced only if necessary.